This invention relates generally to separation of solids from liquids by filtration and in particular to horizontal belt filters in which an endless belt of filter medium is moved intermittently over one or more physically fixed vacuum filtration sections thence to cake discharge and return to filtration.
The type of horizontal belt filter with which this invention is concerned employs a series of fixed vacuum pans over which only the filter medium moves intermittently. One such filter is disclosed in U.S. Pat. No. 3,870,641 in which an endless belt filter medium is moved intermittently (indexed) over the vacuum pans with all movement of the filter medium being effected by a combination that includes one or more continuously rotating drive rollers in contact with the belt and at least two separate, but coordinated shiftable rollers. Vacuum is applied to the belt for preset filtration cycles but released for indexing of the belt.
Prior designs of this type filter have been quite successful and are in wide use, but they suffer from the disadvantage of excessive belt wear, stretching and power consumption on account of the continuously driven rollers and indexing systems employed. Also, the use of separate shiftable rollers for indexing requires a complex control system to coordinate the rollers; and continuously driven rollers wear the belt. Such systems are hard on the filter belt and require much operator attention. Additionally, such prior designs have not provided any reliable ways or means to functionally separate adjacent steps such as form, drain, wash, etc.